Given, 1 instruction takes 7 clock cycles to complete execution.
we know, that each micro-operation takes 1 clock cycle to execute, so, indirectly the question is trying to imply that one instruction has 7 micro-operations.
Now, given, there are 140 instructions in an instruction set, so, the total number of micro-operations is 140*7 = 980 micro-operations.
we know, that each micro-operation is equivalent to a control word in the control memory, so there is a total of 980 control words in the control memory.
So, address size of the control memory = log(980) base2 = 10 bits
according to the format of Control word, number of bits in Control word = number of bits of control signal + number of bits of address size = 126(given data) + 10 = 135 bits
therefore, answer is Option D